Semiconductor laser devices employing a nitride semiconductor, typified by gallium nitride (GaN), are important elements which are used as, for example, light sources for high-density optical disk apparatuses, typified by Blu-ray™ disk apparatuses, light sources for laser display apparatuses, and the like. Blu-ray™ disk apparatuses employ blue-violet light having a wavelength of about 405 nm, while laser display apparatuses employ blue light having a wavelength of about 450 nm. In the field of optical disk apparatuses, there is a demand for light output of several hundred milliwatts for the purpose of an improvement in recording speed and an improvement in reliability of multilayer recording. In the field of laser display apparatuses, there is a demand for light output of several watts for the purpose of an improvement in the luminance of the screen.
Formation of the cavity facet is important in extracting high-power laser light from a semiconductor laser device. The cavity facet is typically formed by cleavage of crystal. Therefore, a high density of dangling bonds (or unsaturated bonds) is formed on the facet. The dangling bond functions as a nonradiative recombination center. In the facet portion, because carriers injected in the active layer are lost at the nonradiative recombination centers, heat is locally generated to a higher degree in the facet portion than in an inner portion of the cavity. An increase in temperature due to the heat generation reduces the width of the forbidden band in the facet portion, and therefore, oscillating laser light which bounces back and forth in the cavity is absorbed by the facet portion. Because the absorbed oscillating laser light increases the temperature of the facet portion, the width of the forbidden band is further reduced. The reduction of the width of the forbidden band due to the heat generation and the increase of the light absorption repeatedly occur, resulting in a local increase in temperature at the facet portion which is accompanied by melting of crystal. This phenomenon is called catastrophic optical damage (COD).
There is a known structure called a facet window structure, in which the width of the forbidden band of the active layer is larger at the facet portion of the cavity than at the inner portion of the cavity so that COD is reduced or prevented. Formation of the facet window structure can effectively reduce or prevent light absorption at the facet portion, resulting in reduction or prevention of the local temperature increase. For gallium arsenide (GaAs)-based laser devices, the facet window structure is implemented by a technique of amorphizing the active layer by diffusing or ion-implanting an impurity (see, for example, Patent Document 1). For example, in the case of the impurity diffusion technique, a metal impurity layer containing zinc (Zn) or the like having a large diffusion constant is formed in a portion corresponding to the facet portion, and the metal impurity is thermally diffused to the active layer. As a result, a region around the active layer is amorphized to form the facet window structure having a large width of the forbidden band.